To provide comfort for truck drivers and reduce driving fatigue experienced by operators of truck vehicles, it is desirable to suspend the operator's cab by utilizing vibration dampening and shock absorption device intermediate the truck chassis and cab which reduces the shock, vibration and consequent pounding the driver experiences during the operation of the vehicle. Additionally, the continued application of vibration and shock forces to the cab results in structural damage which ultimately results in increased maintenance cost.
The load carried by a truck vehicle is supported by the frame which is resiliently carried by suspension springs and supported by the truck wheels. Suspension springs have a high rate of stiffness which makes the ride more jarring on the operator of the vehicle. To dampen the vibration and shock transmitted to the cab, suspension systems have been employed utilizing conventional hydraulic automotive shock absorbers and air springs to dampen jounce and rebound movement of the cab with respect to the truck frame.
Typically, air springs and shock absorbers have been connected directly to the longitudinal side beam members of the truck frame such that the forces transmitted to the cab were located at points remote from the cab center of gravity and consequently resulted in substantial rolling movements in cab sway. For example, U.S. Pat. No. 3,944,017, provides a suspension device for a truck cab having air springs with a low spring rate to isolate the vibration of the vehicle frame from the cab, but did not eliminate such rolling movement.
Further improved devices having combinations of air springs and shock absorbers positioned such that the vibration forces transmitted from the vehicle frame to the truck cab were substantially reduced, are also provided in U.S. Pat. Nos. 4,989,684 and 5,109,939.